Ontogenetic changes in movement patterns and activity levels of American lobsters (Homarus americanus) in Anse-Bleue, southern Gulf of St. Lawrence

Abstract

In this study, the activity and movements of juvenile, adolescent, and adult American lobsters (Homarus americanus) were simultaneously quantified for the first time, using two complementary ultrasonic telemetry tracking systems. Fourteen lobsters measuring 28 to 80.5 mm in carapace length were first tracked for two blocks of 14 days starting in late summer 2011 on a shallow nursery ground in Anse-Bleue, southern Gulf of St. Lawrence, Canada. Tagged lobsters were simultaneously tracked at a fine scale (≈5000 m2) using a VEMCO VRAP ultrasonic telemetry system, and at a larger scale (≈2.5 km2) using an array of 38 VEMCO VR2 receivers. Subsequent monitoring of individuals continued for an additional 58 days (72 total) within the larger VR2 array. Juvenile, adolescent and adult lobsters displayed diurnal activity rhythms, being significantly more active at night than during the day, and they behaved as “central place foragers”, undergoing excursions from and to a “central” shelter area. These behaviours were not found to be affected by body size. In contrast, average daily home range increased gradually with increasing body size, and study-length displacements showed a dichotomy between juveniles and adolescents/adults. Most (7/8) adolescent and adult lobsters moved to deeper water as water temperature decreased in the fall, whereas the juveniles (6/6) stayed in shallow water near the VRAP triangle for the duration of the study. This study provides rare empirical data concerning the movement and behavioural ecology of American lobsters on shallow nursery grounds, and it reveals ontogenetic changes in daily and seasonal movements over the juvenile, adolescent and adult life stages.